Weather Report: Tom Skilling 7-Day Forecast WGN-TV Weather Center.

Ask Tom Why

October 04, 2006|By Tom Skilling

Dear Tom,

Why do tornadoes turn clockwise instead of counterclockwise?

Sarah Sniegowski, St. Isadore School, West Chicago, Ill.

Dear Sarah,Winds spiral in clockwise fashion in only 5-10 percent of tornadoes, and counterclockwise in 90-95 percent.The direction of tornadic air motion is dominated by the Coriolis effect, a phenomenon which dictates that motions in the Northern Hemisphere always experience a deflection to the right of the intended path. When air blows inward, as it does in a tornado, rightward deflection establishes a counterclockwise inward spiral.The Coriolis effect is large in circulations more than 10 miles across, dictating counterclockwise flow. But when tornadoes form in smaller circulations only a few miles in diameter, Coriolis is not so dominant and clockwise flow can sometimes occur. Antlophobia: The irrational or morbid fear of floods.

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Tom Skilling is chief meteorologist at WGN-TV. His forecasts can be seen Monday through Friday on WGN-TV News at noon and 9 p.m.